Storage stable unsaturated thermosettable resins and cured products

ABSTRACT

Thermosettable ethylenically unsaturated resins are rendered storage stable by the addition of a complex formed by mixing (a) at least one quinonoid compound and (b) at least one imidazole compound. The reactivity of these storage stable resins with curing agents is not significantly reduced by the presence of the stabilizer complex.

FIELD OF THE INVENTION

The present invention concerns an additive for thermosettable resins, such resins containing the additive, curable compositions and articles prepared therefrom.

BACKGROUND OF THE INVENTION

Many types of inhibitors are employed to enhance the shelf-stability of liquid thermosettable resins such as unsaturated polyester resins and vinyl ester resins. Examples of these inhibitors include hydroquinone and its alkylated derivatives, phenolic compounds with electron-withdrawing substituents such as nitro, nitroso, or halo moieties, and quinonoid compounds such as para-benzoquinone or para-chloranil.

These compounds enhance the shelf stability of the resin by preventing premature polymerization resulting in the resin becoming an unusable gelatinous mass during storage. However, the addition of such inhibitors to the resin formulation also reduces the ability of the resin to effectively cure during processing. Normally, the shelf stability of the resin must be balanced against the reactivity required for the intended application.

Some of this loss in reactivity may be overcome by the addition of accelerators such as N,N-dimethylaniline, N,N-dimethyl-para-toluidine, or N,N-dimethylacetoacetamide. These compounds accelerate the rate of initiator decomposition and thereby enhance the rate of curing. However, many of these accelerators are unstable if used as an additive in a pre-formulated resin, and may "poison" the cure of the resin by decomposing the initiator too quickly and providing too many radicals of low molecular weight which then forms an incompletely cured resin.

Synergists are compounds which interact together such that the combination of two or more additives mutually enhance the desired performance of each other. Such an example is the addition of phosphite esters in the presence of alkylphenols as antioxidants for polymers and drying oils. Another is the combination of oxalic acid dihydrate and phenothiazine to enhance the storage stability of vinyl ester resins.

Many types of quinonoid compounds have been known to form electron donor-acceptor complexes with compounds such as amines, alkylated polynuclear aromatic compounds, and many other types of polynuclear aromatic compounds. Quinonoid compounds have long been known to be most effective polymerization inhibitors; however, their use as shelf-stability enhancers have been severely limited by their drastic reduction of the desired polymerization rate and would require an impractical amount of initiator and accelerator to effectively complete the curing process. The addition of imidazole derivatives, which only act as weak accelerators in this process, serve to enhance both the shelf-stability and reactivity in the presence of many quinonoid compounds to a greater degree than would be found with inhibitors which do not form electron-donor acceptor complexes.

It would therefore be desirable to have available storage stable thermosettable ethylenically unsaturated resins which also have suitable reactivity rates with curing agents therefor.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to a polymerization inhibitor concentrate which comprises (1) at least one polymerizable ethylenically unsaturated monomer; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound.

Another aspect of the present invention pertains to a polymerization inhibitor concentrate which comprises (1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound.

Another aspect of the present invention pertains to a storage stable thermosettable ethylenically unsaturated resin composition comprising (1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound wherein component (2) is present in an amount sufficient to render the composition storage stable.

Another aspect of the present invention pertains to a curable composition comprising (I) a resin composition comprising (1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound; wherein component (2) is present in an amount sufficient to render a composition containing component (I) free of component (II) storage stable; and (II) a curing amount of at least one curing agent for component (I).

A further aspect of the present invention pertains to an article resulting from curing the aforementioned curable composition.

The present invention provides storage stable thermosettable ethylenically unsaturated resins which also have suitable reactivity rates with curing agents therefor.

DETAILED DESCRIPTION OF THE INVENTION

The polymerization inhibitor concentrate compositions of the present invention which comprise (1) at least one polymerizable ethylenically unsaturated monomer; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound usually contain from about 50 to about 99.9, preferably from about 90 to about 99.9, more preferably from about 95 to about 99.9 percent by weight of component (1) based upon the combined amount of components (1) and (2) and from about 0.1 to about 50, preferably from about 0.1 to about 10, more preferably from about 0.1 to about 5 percent by weight of component (2) based upon the combined amount of components (1) and (2).

The polymerization inhibitor concentrate compositions of the present invention which comprise (1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound usually contain from about 50 to about 99.9, preferably from about 90 to about 99.9, more preferably from about 95 to about 99.9 percent by weight of component (1) based upon the combined amount of components (1) and (2) and from about 0.1 to about 50, preferably from about 0.1 to about 10, more preferably from about 0.1 to about 5 percent by weight of component (2) based upon the combined amount of components (1) and (2).

In the storage stable thermosettable ethylenically unsaturated resin composition comprising (1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from (a) at least one quinonoid compound and (b) at least one imidazole compound, component (2) is present in an amount sufficient to render the composition storage stable, usually contain from about 5 to about 20,000, preferably from about 50 to about 10,000, more preferably from about 100 to about 5,000 parts per million by weight (ppm) of component (2) based upon the combined amount of components (1) and (2).

The complex between the quinonoid compound and the imidazole compound can be prepared by admixing the two components in solution in a solvent such as methylene chloride, dimethylsulfoxide, methanol, ethanol, acetone or combinations thereof and the like at a temperature of from about -20° C. to about 60° C., preferably from about -5° C. to about 30° C. for a time sufficient to form the complex, usually form about 0.1 to about 48, preferably from about 0.5 to about 24, more preferably from about 1 to about 12 hours. The product may be isolated by precipitation from solution.

If desired, the complex can be formed by adding the two components separately to either the thermosettable ethylenically unsaturated resin or polymerizable ethylenically unsaturated monomer or a mixture thereof and forming the complex in situ. Preparing the complex in this manner will usually require a much longer period of time due to the dilution effect of the resin and or monomer.

Also, the complex can be preformed before adding to either the monomer or ethylenically unsaturated polymer or combination thereof.

The quinonoid compound, component (2a), and the imidazole compound, component (2b), are suitably employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1, preferably from about 0.5:1 to about 20:1, more preferably from about 1:1 to about 10:1.

Suitable quinonoid acceptor compounds which can be employed herein include any mononuclear or polynuclear ring compounds containing two ketone oxygen atoms in the molecule. Likewise, the term "quinonoid" as employed herein means a compound which is a mononuclear or polynuclear ring compound which contains two ketone oxygen atoms attached to different carbon atoms in the ring in mononuclear ring compounds or different carbon atoms in the same ring or a different ring in polynuclear compounds. The term "mononuclear" means a compound containing a single ring structure whereas the term "polynuclear" means a compound containing more than one ring structures. It is preferred that the "polynuclear" compounds be composed of fused rings.

Suitable such compounds include those represented by the following formulas I, II, III, IV and V ##STR1## wherein each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20, preferably from 1 to about 10, more preferably from 1 to about 4 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20, preferably from 1 to about 10, more preferably from 1 to about 3 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 5, more preferably from about 1 to about 3. Particularly suitable such quinonoid electron acceptor compounds include, for example, 1,4-benzoquinone, 1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, 2,3-dibromo-1,4-naphthoquinone, 3-chloro-2-bromo-1,4-naphthoquinone, 6-chloro-1,4-naphthoquinone, 2-bromo-1,4-naphthoquinone, 5,8-dichloro-1,4-naphthoquinone, 2,3,5,4,6,7,8-hexachloro-1,4-naphthoquinone, 5-bromo-1,4-naphthoquinone, combinations thereof and the like.

The 1,4-naphthoquinone compounds substituted in the 2 or 3 or both the 2 and the 3 positions without being complexed or reacted with an electron donor compound can provide the ethylenically unsaturated resin with enhanced storage stability with a suitable reactivity for some applications. A particularly suitable such compound is 2,3-dichloro-1,4-naphthoquinone, 2,3-dibromo-1,4-naphthoquinone, 2,3-dicyano-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, 2-bromo-1,4-naphthoquinone, 2-nitro-1,4-naphthoquinone, 2,3,6,7,8,9-hexachloro-1,4-naphthoquinone, 3-bromko-2-chloro-1,4-naphthoquinone, any combination thereof and the like.

Suitable electron donor imidazole compounds which can be employed herein include, for example, those represented by the following formulas VI, VII or VIII ##STR2## wherein each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20, preferably from 1 to about 10, more preferably from 1 to about 6 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20, preferably from 1 to about 10, more preferably from 1 to about 6 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 6, more preferably from about 1 to about 3; R^(b) and R" are independently hydrogen, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20, preferably from 1 to about 10, more preferably from 1 to about 3 carbon atoms, or a cyano alkyl group having from about 2 to about 6 carbon atoms.

Particularly suitable imidazole electron donor compounds which can be employed herein include, for example, 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptadecylimidazole, 2-(2-ethyl-4-methylimidazoyl)-1-cyanoethane, 1-benzyl-2-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, combinations thereof and the like.

If desired, the stabilizer complexes of the present invention can be employed in combination with the known stabilizers such as, for example, 1,4-hydroquinone, 4-tertiary-butylcatechol, 4-methoxyhenol, methylhydroquinone, 4-chloro-2-nitrophenol, 2,4-dinitropara-cresol,2,4-dinitrophenol, phenothiazine, oxalic acid, maleic acid, combinations thereof and the like. When employed, these known stabilizers are employed in an amount of from about 5 to about 5,000, preferably from about 25 to about 1,000, more preferably from about 50 to about 400 parts per million based upon the combined weight of thermosettable resin, polymerizable ethylenically unsaturated monomers and stabilizers.

They can also be employed in combination with acids such as oxalic acid which, if desired, can be hydrated, or nitric acid.

Particularly suitable thermosettable resins which contain ethylenically unsaturated groups which can be employed herein include, for example, vinyl ester resins, unsaturated polyester resins, vinyl urethane resins, combinations thereof and the like.

Particularly suitable vinyl ester resins include, for example, those prepared by reacting a polyepoxide with an unsaturated monocarboxylic acid. Particularly suitable such vinyl ester resins and methods for their preparation are disclosed in U.S. Pat. Nos. 3,367,992; 3,066,122; 3,179,623; 3,301,753; 3,256,226; 3,564,074; 3,892,819; 4,407,991 and 4,594,398; all of which are incorporated herein by reference in their entirety.

Also suitable are the vinyl ester resins which contain dicyclopentadiene or other dienes and oligomers thereof as described by Nelson et al. in U.S. Pat. Nos. 4,525,544 and 4,594,398 which are incorporated herein by reference in their entirety.

The vinyl ester resins can be modified with any suitable rubber or elastomer. Suitable rubbers or elastomers include, for example, carboxyl-containing rubbers or elastomers, copolymers of alkyl acrylates or methacrylates or alkyl esters of other alpha-alkyl rubber particles characterized by having a rubbery core and a grafted polymer shell which is compatible with vinyl ester resins. Vinyl ester resins can be modified with a carboxyl-containing rubber or elastomer by the method disclosed by D. J. Najvar in U.S. Pat. No. 3,892,819 which is incorporated herein by reference. These rubbers or elastomers containing acrylate, vinyl, secondary amine groups, or carboxyl-containing moieties are commercially available from the B. F. Goodrich Company under the tradename of HYCAR.

Other particularly suitable forms of rubber or elastomer for modification of the vinyl ester compositions of the present invention include poly(alkylacrylate) or poly(alkylmethacrylate polymers as produced by the methods disclosed by D. K. Hoffman et al. in U.S. Pat. No. 4,690,988, monomers polymerized in situ in the epoxy resin to form a stable polymer phase as disclosed by D. Hoffman and C. Arends in U.S. Pat. No. 4,708,996 issued Nov. 24, 1987 and also by R. E. Adam et al. in U.S. Pat. No. 4,524,181, and rubbers or elastomers available in the form of grafted rubber concentrates as described by D. E. Henton, et al. in U.S. Pat. No. 4,778,851, issued Oct. 18, 1988.

Particularly suitable unsaturated polyester resins include, for example, those prepared by reacting an unsaturated polycarboxylic acid with a polyfunctional alcohol (polyol). Particularly suitable such polyester resins and methods for their preparation include those disclosed in U.S. Pat. Nos. 2,627,510, 2,632,751, 2,945,837, 3,775,513 and 3,901,953, all of which are incorporated herein by reference in their entirety.

Also suitable are polyester resins which contain dicyclopentadiene or other dienes and oligomers thereof as described by D. L. Nelson in U.S. Pat. No. 4,148,765 which is incorporated herein by reference in its entirety.

Particularly suitable unsaturated vinyl urethane resins which can be employed herein include, for example, those prepared by reacting a hydroxyl terminated polyester resin with a multifunctional isocyanate and a hydroxyalkylacrylate. Particularly suitable such unsaturated vinyl urethane resins and methods for their preparation include, for example, those described in U.S. Pat. Nos. 3,876,726, 4,287,116 and 4,524,178 which are incorporated herein by reference in their entirety.

The unsaturated polyester resins and the vinyl urethane resins can also be modified with rubbers or elastomers as described for the vinyl ester resins.

If desired, these thermosettable unsaturated resins can be diluted or blended with a polymerizable ethylenically unsaturated monomer. Suitable such monomers include, for example, vinyl aromatic compounds; saturated or unsaturated aliphatic or cycloaliphatic esters of ethylenically unsaturated monocarboxylic acids wherein the ester portion of the monomer contains from 1 to about 20, preferably from about 1 to about 10, more preferably from about 1 to about 5 carbon atoms and the acid portion of the monomer contains from about 3 to about 10, preferably from about 3 to about 8, more preferably from about 3 to about 4 carbon atoms; combinations thereof and the like. Particularly suitable such polymerizable ethylenically unsaturated monomers include, for example, those disclosed in the aforementioned U.S. Pat. Nos. 3,892,819 and 4,594,398, particularly suitable are aromatic compounds such as, for example, styrene, α-methylstyrene, dichlorostyrene, vinyl naphthalene, vinyl toluene, divinylbenzene, vinyl acetate, vinyl benzoate, vinyl chloroacetate,; unsaturated esters such as esters of acrylic and methacrylic acid, vinyl acetate, vinyl benzoate, vinyl chloroacetate, vinyl laurate and the like; unsaturated acids such as, for example, acrylic acid, alpha-alkylacrylic acid, butenoic acid, allylbenzoic acid, vinylbenzoic acid, and the like; unsaturated organic halides such as, for example, vinyl chloride, vinylidene chloride, and the like; nitriles such as acrylonitrile, methacrylonitrile, and the like, diolefins such as, for example, butadiene, isoprene, methylpentadiene, and the like; esters of polycarboxylic acids such as, for example, diallyl phthalate, divinyl succinate, diallyl maleate, divinyl adipate, dichloroallyl tetrahydrophthalate, and the like; and any combinations of any two or more of such monomers and the like.

These polymerizable ethylenically unsaturated monomers can be employed in any desired amount so as to reduce the viscosity of the composition; however, they are usually employed in amounts of from about zero to about 60, preferably from about 10 to about 55, more preferably from about 20 to about 50 percent by weight based upon the combined weight of thermosettable unsaturated resin and polymerizable ethylenically unsaturated monomer.

These stabilized thermosettable unsaturated resins can be cured with conventional curing agents or curing catalysts which generate free radicals such as, for example, organic peroxides, azo compounds, combinations thereof and the like. Particularly suitable such curing agents or curing catalysts include, for example, the peroxides such as, for example, benzoyl peroxide, tertiary-butyl hydroperoxide, ditertiary-butyl peroxide, hydrogen peroxide, potassium persulfate, methyl cyclohexyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, acetyl benzoyl peroxide, tetralin hydroperoxide, phenylcyclohexane hydroperoxide, tertiary-butyl perbenzoate, ditertiary-amyl perphthalate, ditertiary-butyl peradipate, tertiary-amyl percarbonate, bis(4-tertiary-butylcyclohexyl)peroxydicarbonate, and the like; and azo compounds such as, for example, 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis(2,4-dimethylvaleronitrile, 2,2'-azobisisotoluylamide, and the like. Combinations of any two or more of the above curing catalysts or curing agents can be employed if desired.

These curing agents are employed in any amount which is sufficient to effect the cure of the stabilized thermosettable unsaturated resins; however, usually amounts of from about 0.1 to about 5, preferably from about 0.1 to about 3, percent by weight based upon total resin weight is sufficient to effect the cure. It should be noted, however, that the optimum amount of curing agent will vary depending upon the curing agent and the stabilized thermosettable unsaturated resin being employed.

If desired, accelerators or promoters for these curing agents or curing catalysts can be employed. Suitable such accelerators or promoters include metal salts of carboxylic acids such as, for example, cobalt naphthenate, or vanadium neodecanoate either alone or in combination with tetriary amines such as, for example, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethylacetoacetamide, N,N-dimethyl-para-toluidine, and the like.

The accelerators are suitably employed in amounts of from about 0.02 to about 1, more suitably from about 0.05 to about 0.6 percent by weight based on total resin weight.

If desired, the compositions of the present invention can contain reinforcing materials in the form of mats, woven fabric, unidirectional fibers, rovings, random fibers or filaments, inorganic fillers, inorganic whiskers, hollow spheres, ceramic and glass spheres and the like. These reinforcing materials can be prepared from glass fibers, aramid fibers, graphite fibers, and polymer fibers such as, for example, nylon, polyalkyleneterephthalate, polyethylene, polypropylene, polyesters, combinations thereof and the like.

If desired, other components can be included in the compositions of the present invention, such as, for example, pigments, dyes, fillers, wetting agents, chemical thickeners, fire retardant additives, emission suppressants for monomer vapors, adhesion promoters, and the like. These components are included in amounts which are effective for their purpose, e.g. pigments and dyes are employed in amounts sufficient to color the composition to the extent desired, wetting agents are employed in amounts sufficient to wet out any reinforcing materials present in the composition.

The curable compositions of the present invention can be employed in the preparation of laminates or composites which are useful in the construction of storage vessels, automobiles, airplanes, and other structures and structural parts that can be produced via filament winding, pultrusion, braiding and resin transfer molding. Further uses include, for example, tank and vessel liners, coatings, polymer concrete, potting or encapsulating formulations, and the like.

The following examples are illustrative of the present invention, but are not to be construed as to limiting the scope thereof in any manner.

The following thermosettable resins are employed in the examples.

Thermosettable Resin A is a vinyl ester resin having an acid number not greater than 10, a viscosity at 25° C. of 2200-2700 centistokes, an SPI gel time at 180° F. of 7.0-12.0 minutes, a Gardner color not greater than 4, and a density of 1.068-1.078 g/ml. This resin is commercially available from The Dow Chemical Company as DERAKANE™ 411-35LI vinyl ester resin, lot no. AJ890216901.

Thermosettable Resin B is a vinyl ester resin prepared in the following manner.

A reactor is charged with 2,816.4 g of diglycidyl ether of bisphenol A having an EEW of 181 and 1,488.1 g of tetrabromobisphenol A. The resin is heated at 150° C. for 1.5 hours with 2.39 g of a 70% methanolic solution of ethyltriphenylphosphonium acetate.acetic acid complex with a nitrogen sparge. The resultant advanced epoxy rein is reacted with 886 g of glacial methacrylic acid in the presence of air and 400 ppm of hydroquinone at 110° C. in the presence of 6.6 grams of 2,4,6-tri(N,N-dimethylamino)phenol as a catalyst until a 1.1% acid concentration is reached. The resultant vinyl ester resin is dissolved in styrene such that the resultant mixture has a styrene content of 30% by weight.

Thermosettable Resin C is Thermosettable Resin B with additional amounts of styrene such that the total amount of styrene is 35% by weight based on total weight of the resin.

Thermosettable Resin D is a vinyl ester resin having an acid number not greater than 10, a viscosity at 25° C. of 2200-2700 centistokes, an SPI gel time at 180° F. of 7.0-12.0 minutes, a Gardner color not greater than 4, and a density of 1.068-1.078 g/ml. This resin is commercially available from The Dow Chemical Company as DERAKANE™ 411-35LI vinyl ester resin, lot no. AJ890613902.

The following quinonoid electron acceptor compounds are employed in the examples.

Quinonoid Compound A is 1,4-benzoquinone.

Quinonoid Compound B is 1,4-naphthoquinone.

Quinonoid Compound C is 2,3,5,6-tetrachloro-1,4-benzoquinone.

Quinonoid Compound D is 2,3-dichloro-1,4-naphthoquinone.

Quinonoid Compound E is 2,3-dimethoxy-5-methylbenzoquinone.

Quinonoid Compound F is plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone).

Quinonoid Compound G is 3,4,5,6-tetrachloro-1,2-benzoquinone.

The following imidazole electron donor compounds are employed in the examples.

Imidazole Compound A is 1,methylimidazole.

Imidazole Compound B is 2-ethyl-4-methylimidazole.

Imidazole Compound C is benzimidazole.

Imidazole Compound D is 2-phenylimidazole.

Imidazole Compound E is 2-(2-ethyl-4-methylimidazyl)-1-cyanoethane.

Imidazole Compound F is 1-benzyl-2-methylimidazole.

Other Inhibitors and Additives (OIA) employed in the examples are as follows.

Preformed Complex BA is prepared by dissolving 15.84 g (0.1002 mole) of 1,4-naphthoquinone (quinonoid compound B) in 300 ml of methylene chloride. The flask containing the solution is fitted with a reflux condenser, placed in an ice/water bath, and cooled to 3° C. with stirring by a magnetic stirring bar. 1-Methylimidazole (imidazole compound A), 8.66 g (0.1055 mole), is then added to the quinone solution in two portions (3.81 g and 4.85 g) over a 15 minute period. After each addition the temperature increases by about 10° C. and is allowed to cool back down to 2° to 4° C. The solution is maintained at a temperature of 4° to 6° C. for another 4.5 hours and is allowed to set overnight at ambient temperature. The methylene chloride and excess 1-methylimidazole is evaporated off first on a hot plate and then in a vacuum oven at 60° C. for about 20 minutes. A black tarry precipitate is recovered which is soluble in acetone, methanol, slightly soluble in hot water and dilute acetic acid, and insoluble in toluene. The proton magnetic resonance spectrum of the product in deuterated dimethylsulfoxide indicates that the aromatic ring protons of the 1,4-naphthoquinone at 7.85 ppm (splitting constants 5.5, 3.5 Hz) has shifted to about 8.3 ppm and broadened to 60 Hz overall. The imidazole peaks are present at 7.4, 7.0, 6.8, and 3.6 ppm.

EXAMPLES 1-27

Various thermosettable resins are inhibited with various inhibitor compositions. These inhibited compositions are prepared by blending the indicated resin with the indicated inhibitor composition at a temperature of 25° C. In the case of the inhibitor complexes of the present invention, the complex is formed prior to blending it with the thermosettable resin. The inhibitor complex is formed by blending the electron donor and electron acceptor compounds together at a temperature of 25° C. for about 24 to 120 hours.

The blended compositions are given in Table I.

The blended compositions are subjected to the following tests.

STORAGE STABILITY

These compositions are tested for storage stability by placing the composition in a two ounce (59.1 ml) narrow mouth round amber bottle filled to the indicated volume and capping the thus filled bottle with 20 mm tin lined plastic caps. The bottles are placed in an air circulated oven maintained at the indicated temperature. The stability of the resin is checked daily by inverting the bottles. A sample is considered to be gelled and the test terminated when a layer of solid resin remains at the bottom of the bottle or when the sample appears stringy in consistency. The time in days required for the sample to gel is recorded.

REACTIVITY (GEL TIME & CURE TIME)

A 0.4 gram sample of benzoyl peroxide curing agent is mixed with 0.2 gram of styrene in a 100 ml tripour beaker. A 40 gram sample of the resin composition is introduced and mixed thoroughly with a wooden spatula. The thus catalyzed resin is poured into each of two 18 mm×150 mm test tubes to a level of 3 inches (76 mm). The test tubes are allowed to stand for 10 to 20 minutes to be rid of air bubbles. A thermocouple is inserted into the center of the resin composition to one inch (25.4 mm) below the resin surface. The test tube is placed in a constant temperature bath maintained at 150° F. (82.2° C.). The temperature change as a function of time is recorded on a microprocessor. The initial time is marked when the resin is heated to 150° F. (65.6° C.). The time required to reach 190° F. (87.7° C.) is recorded as the gel time. The test is continued until the recorder has run two minutes past the maximum temperature. The maximum temperature is the peak exother. The time required to reach the peak exotherm is recorded as the cure time.

The results are given in Table I.

                                      TABLE I                                      __________________________________________________________________________                   Example Number                                                   Component & Property                                                                         Ex. 1                                                                               Ex. 2                                                                               Ex. 3                                                                               Ex. 4                                                                               Ex. 5                                                                               Ex. 6                                                                               Ex. 7                                                                               Ex. 8                                                                               Ex.                                                                                Ex.                  __________________________________________________________________________                                                               10                   Thermosettable Resin                                                                         A    A    A    A    A    A    B    C    C   A                    Quinonoid Compound, Type                                                                     A    A    B    B    C    D    B    A    B   D                      conc. (ppm) 136  136  199  202  311  287  201  138  200 286                  Imidazole Compound, Type                                                                     A    B    A    B    A    A    A    A    A   --                     conc. (ppm) 744  1039 759  998  752  747  719  754  735                      Oxalic Acid Dihydrate, ppm                                                                   202  200  199  199  200  200  200  200  200 203                  Other Additive, Type                                                                         --   --   --   --   --   --   --   --   --  --                     conc. (ppm)                                                                  Shelf Stability                                                                94% filled @ 55° C., days                                                              8    5    9    8    3    7    4    6    4   7                   70% filled @ 55° C., days                                                              15   11  9.5   9    14    8   4    17   5   6                   94% filled @ 43° C., days                                                              23   17   28   23  13.5  26  12.5  20  13.5                                                                                28                  Gel Time, minutes                                                                            4.70 6.50 7.06 6.59 6.92 6.26 8.24 11.84                                                                                8.99                                                                              6.2                  Cure Time, minutes                                                                           6.50 8.40 8.94 8.65 8.95 7.98 10.72                                                                               13.66                                                                               11.79                                                                               8.23                Peak Exotherm, °F.                                                                    378  376  371  366  369  376  363  369  374 370                         , °C.                                                                          192.2                                                                               191.1                                                                               188.3                                                                               185.6                                                                               187.2                                                                               191.1                                                                               183.9                                                                               187.2                                                                               190 187.8                __________________________________________________________________________                   Example Number                                                                 Ex.  Ex.  Ex.  Ex.  Ex.  Ex.  Ex.  Ex.  Ex. Ex.                  Component & Property                                                                         11   12   13   14   15   16   17   18   19  20                   __________________________________________________________________________     Thermosettable Resin                                                                         D    D    D    D    D    D    D    D    D   D                    Quinonoid Compound, Type                                                                     A    B    D    A    B    D    B    B    B   A                      conc. (ppm) 136  200  287  136  200  287  200  200  200 137                  Imidazole Compound, Type                                                                     A    A    A    C    C    C    D    E    F   A                      conc. (ppm) 750  750  750  1,080                                                                               1,080                                                                               1,080                                                                               965  1,490                                                                               1,450                                                                              748                  Oxalic Acid Dihydrate, ppm                                                                   --   --   --   --   --   --   --   --   --  --                   Other Additive, Type                                                                         --   --   --   --   --   --   --   --   --  --                     conc. (ppm)                                                                  Shelf Stability                                                                94% filled @ 55° C., days                                                              3    8   6.5   3    8    8    6   6.5   6   3                   70% filled @ 55° C., days                                                              5   9.5   6    6    10  8.5  6.5  7.5   8   5                   94% filled @ 43° C., days                                                             --   --   --   --   --   --   --   --   --  --                   Gel Time, minutes                                                                             8.15                                                                                9.83                                                                               10.6 13.53                                                                               14.81                                                                               12.00                                                                               12.72                                                                               12.25                                                                                9.45                                                                              5.95                 Cure Time, minutes                                                                           10.26                                                                               12.36                                                                               12.98                                                                               15.81                                                                               17.80                                                                               14.78                                                                               15.28                                                                               14.63                                                                               11.85                                                                              8.06                 Peak Exotherm, °F.                                                                    362  359  360  361  348  363  362  367  372 375                         , °C.                                                                          183.3                                                                               181.7                                                                               182.2                                                                               182.8                                                                               175.6                                                                               183.9                                                                               183.3                                                                               186.1                                                                               188.9                                                                              190.6                __________________________________________________________________________                                  Example Number                                                                 Ex.  Ex.  Ex.  Ex.  Ex.  Ex. Ex.                                 Component & Property                                                                         21   22   23   24   25   26  27                   __________________________________________________________________________                    Thermosettable Resin                                                                         D    D    D    D    A    A   A                                   Quinonoid Compound, Type                                                                     D    D    E    F    G    --  --                                    conc. (ppm) 287  1,036                                                                               229  235  310                                          Imidazole Compound, Type                                                                     --   --   A    A    A    --  A                                     conc. (ppm)           777  760  750      624                                 Oxalic Acid Dihydrate, ppm                                                                   --   --   --   --   203  200 200                                 Other Additive, Type                                                                         --   --   --   --   --   BA  BA                                    conc. (ppm)                          313 314                                 Shelf Stability                                                                94% filled @ 55° C., days                                                              8    13  >9   4.5  4.5   7   6                                  70% filled @ 55° C., days                                                              7   12.5 > 9   5    13  --  --                                  94% filled @ 43° C., days                                                             --   --   --   --    16  --  --                                  Gel Time, minutes                                                                            12.82                                                                               13.17                                                                               19.04                                                                                9.14                                                                               6.64 7.38                                                                               6.17                                Cure Time, minutes                                                                           15.46                                                                               16.24                                                                               21.18                                                                               11.55                                                                               8.52 9.46                                                                               7.97                                Peak Exotherm, °F.                                                                    356  340  344  368  370  371 370                                        , °C.                                                                          180  171.1                                                                               173.3                                                                               186.7                                                                               187.8                                                                               188.3                                                                              187.8                __________________________________________________________________________

The above data clearly illustrates that the stabilizer system of the present invention provides shelf stability for the unsaturated thermosettable resins without an unacceptable decrease in reactivity when the stabilized unsaturated thermosettable resins are blended with a curing agent and cured. 

What is claimed is:
 1. A polymerization inhibitor concentrate which comprises(1) at least one polymerizable ethylenically unsaturated monomer; and (2) a complex formed from(a) at least one quinonoid compound represented by the following formulas I-V ##STR3## wherein each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10; and (b) at least one imidazole compound represented by the following formulas VI-VIII ##STR4## wherein each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 6; R^(b) and R" are independently hydrogen, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or a cyano alkyl group having from about 2 to about 6 carbon atoms; and wherein components (2a) and (2b) are employed in amounts which provide a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1.
 2. A polymerization inhibitor concentrate of claim 1 wherein component (1) is present in an amount of from about 50 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 50 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1.
 3. A polymerization inhibitor concentrate of claim 1 wherein component (1) is present in an amount of from about 90 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 10 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 20:1.
 4. A polymerization inhibitor concentrate of claim 1 wherein component (1) is present in an amount of from about 95 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 5 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 1:1 to about 10:1.
 5. A polymerization inhibitor concentrate of claim 1, 2, 3 or 4 wherein said polymerizable ethylenically unsaturated monomer is a vinyl aromatic compound or a saturated or unsaturated aliphatic or cycloaliphatic ester of an ethylenically unsaturated monocarboxylic acid, or any combination thereof.
 6. A polymerization inhibitor concentrate of claim 5 wherein(a) in said quinonoid compound, each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms; and m has a value from 1 to about 5; (b) in said imidazole compound each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 6 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 6 carbon atoms; and m has a value from 1 to about 3; and (c) said polymerizable ethylenically unsaturated monomer is a vinyl aromatic compound or mixture of such compounds.
 7. A polymerization inhibitor concentrate of claim 1, 2, 3 or 4 wherein(a) said quinonoid compound is 1,4-benzoquinone, 1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-1,4-naphthoquinone, or any combination thereof; (b) said imidazole compound is 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or any combination thereof; and (c) said polymerizable ethylenically unsaturated monomer is styrene, vinyl toluene, α-methylstyrene, divinylbenzene, or any combination thereof.
 8. A polymerization inhibitor concentrate which comprises(1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from(a) at least one quinonoid compound ##STR5## wherein each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to ##STR6## about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10; and (b) at least one imidazole compound represented by the following formulas VI-VIII ##STR7## wherein each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 6; R^(b) and R" are independently hydrogen, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or a cyano alkyl group having from about 2 to about 6 carbon atoms; and wherein components (2a) and (2b) are employed in amounts which provide a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1; andwherein component (2) is present in an amount in excess of that required to obtain storage stability.
 9. A polymerization inhibitor concentrate of claim 8 wherein component (1) is present in an amount of from about 50 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 50 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1.
 10. A polymerization inhibitor concentrate of claim 8 wherein component (1) is present in an amount of from about 90 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 10 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 20:1.
 11. A polymerization inhibitor concentrate of claim 8 wherein component (1) is present in an amount of from about 95 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 5 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 1:1 to about 10:1.
 12. A polymerization inhibitor concentrate of claim 8, 9, 10, or 11 wherein said thermosettable ethylenically unsaturated resin is a vinyl ester resin, unsaturated polyester resin, a vinyl urethane resin, or any combination thereof.
 13. A polymerization inhibitor concentrate of claim 12 wherein(a) in said quinonoid compound, each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms; and m has a value from 1 to about 5; (b) in said imidazole compound each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 6; and (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin or unsaturated polyester resin, or any combination thereof.
 14. A polymerization inhibitor concentration of claim 8, 9, 10 or 11 wherein(a) said quinonoid compound is 1,4-benzoquinone, 1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-1,4-naphthoquinone, or any combination thereof; (b) said imidazole compound is 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or any combination thereof; and (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin.
 15. A storage stable thermosettable ethylenically unsaturated resin composition comprising(1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from(a) at least one quinonoid compound represented by the following formulas I, II, III, IV or V ##STR8## wherein each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10; and (b) at least one imidazole compound represented by the following formulas VI-VIII ##STR9## wherein each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 6; R^(b) and R" are independently hydrogen, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or a cyano alkyl group having from about 2 to about 6 carbon atoms; and wherein components (2a) and (2b) are employed in amounts which provide a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1; andwherein component (2) is present in an amount sufficient to render the composition storage stable.
 16. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15 wherein component (2) is present in an amount of from about 5 to about 20,000 parts per million by weight based upon the combined weight of components (1) and (2).
 17. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15 wherein component (2) is present in an amount of from about 50 to about 10,000 parts per million by weight based upon the combined weight of components (1) and (2).
 18. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15 wherein component (2) is present in an amount of from about 100 to about 5,000 parts per million by weight based upon the combined weight of components (1) and (2).
 19. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15, 16, 17, or 18 wherein said thermosettable ethylenically unsaturated resin is a vinyl ester resin, unsaturated polyester resin, a vinyl urethane resin, or any combination thereof.
 20. A storage stable thermosettable ethylenically unsaturated resin composition of claim 19 wherein(a) in said quinonoid compound, each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms; and m has a value from 1 to about 5; (b) in said imidazole compound each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 20 carbon atoms; and m has a value from 1 to about 6; and (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin or unsaturated polyester resin, or any combination thereof.
 21. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15, 16, 17 or 18 wherein(a) said quinonoid compound is 1,4-benzoquinone, 1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-1,4-naphthoquinone, or any combination thereof; (b) said imidazole compound is 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or any combination thereof; and (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin.
 22. A storage stable thermosettable ethylenically unsaturated resin composition of claim 15, 16, 17 or 18 which additionally contains at least one polymerizable ethylenically unsaturated monomer.
 23. A storage stable thermosettable ethylenically unsaturated resin composition of claim 19 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of vinyl aromatic compounds; saturated or unsaturated aliphatic or cycloaliphatic esters of ethylenically unsaturated monocarboxylic acids wherein the ester portion of the monomer contains from 1 to about 20, carbon atoms and the acid portion of the monomer contains from about 3 to about 20 carbon atoms; combinations thereof and the like.
 24. A storage stable thermosettable ethylenically unsaturated resin composition of claim 20 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of vinyl aromatic compounds.
 25. A storage stable thermosettable ethylenically unsaturated resin composition of claim 21 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of styrene, vinyl toluene, α-methylstyrene, divinylbenzene, vinyl naphthalene, dichlorostyrene, combinations thereof and the like.
 26. A curable composition comprising(I) a resin composition comprising(1) at least one thermosettable ethylenically unsaturated resin; and (2) a complex formed from(a) at least one quinonoid compound represented by the following formulas I, II, III, IV or V ##STR10## wherein each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10; and (b) at least one imidazole compound represented by the following formulas VI-VIII ##STR11## wherein each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 10, preferably from about 1 to about 6; R^(b) and R" are independently hydrogen, an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms, or a cyano alkyl group having from about 2 to about 6 carbon atoms; and wherein components (2a) and (2b) are employed in amounts which provide a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1.; wherein component (2) is present in an amount sufficient to render a composition containing component (I) free of component (II) storage stable; and (II) a curing amount of at least one curing agent for component (I).
 27. A curable composition of claim 26 wherein component (1) is present in an amount of from about 50 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 50 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 100:1.
 28. A curable composition of claim 26 wherein component (1) is present in an amount of from about 90 to about 99.1 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 10 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 0.5:1 to about 20:1.
 29. A curable composition of claim 26 wherein component (1) is present in an amount of from about 95 to about 99.9 percent by weight based upon the combined weight of components (1) and (2); component (2) is present in an amount of from about 0.1 to about 5 percent by weight based upon the combined weight of components (1) and (2); and components (2a) and (2b) are employed in a molar ratio of imidazole compound to quinonoid compound of from about 1:1 to about 10:1.
 30. A curable composition of claim 26, 27, 28, or 29 wherein said thermosettable ethylenically unsaturated resin is a vinyl ester resin, unsaturated polyester resin, a vinyl urethane resin, or any combination thereof.
 31. A curable composition of claim 30 wherein(a) in said quinonoid compound, each R is independently hydrogen, a halogen atom such as F, Cl, Br or I, a nitro group, a cyano group, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms; and m has a value from 1 to about 5; (b) in said imidazole compound each R^(a) is independently hydrogen, a cyanoalkyl group having from 1 to about 6 carbon atoms, a hydroxyalkyl group having from 1 to about 6 carbon atoms, an acyclic or a cyclic aliphatic hydrocarbon having from 1 to about 10 carbon atoms, or OR' wherein each R' is independently an acyclic or a cyclic aliphatic hydrocarbon having from about 1 to about 20 carbon atoms; and m has a value from 1 to about 6; and (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin or unsaturated polyester resin, or any combination thereof.
 32. A curable composition of claim 26, 27, 28 or 29 wherein(a) said quinonoid compound is 1,4-benzoquinone, 1,4-naphthoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-1,4-naphthoquinone, or any combination thereof; (b) said imidazole compound is 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or any combination thereof; (c) said thermosettable ethylenically unsaturated resin is a vinyl ester resin; and (d) said curing agent is a peroxygen containing compound.
 33. A curable composition of claim 26, 27, 28 or 29 which additionally contains at least one polymerizable ethylenically unsaturated monomer.
 34. A curable composition of claim 30 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of vinyl aromatic compounds; saturated or unsaturated aliphatic or cycloaliphatic esters of ethylenically unsaturated monocarboxylic acids wherein the ester portion of the monomer contains from 1 to about 20 carbon atoms and the acid portion of the monomer contains from about 3 to about 20 carbon atoms; combinations thereof and the like.
 35. A curable composition of claim 31 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of vinyl aromatic compounds.
 36. A curable composition of claim 32 which additionally contains at least one polymerizable ethylenically unsaturated monomer selected from the group consisting of styrene, vinyl toluene, α-methylstyrene, divinylbenzene, vinyl naphthalene, dichlorostyrene, combinations thereof and the like.
 37. An article resulting from curing the curable composition of claim 26, 27, 28 or
 29. 38. An article resulting from curing the curable composition of claim
 30. 39. An article resulting from curing the thermosettable composition of claim
 31. 40. An article resulting from curing the thermosettable composition of claim
 32. 41. An article resulting from curing the thermosettable composition of claim
 33. 42. An article resulting from curing the thermosettable composition of claim
 34. 43. An article resulting from curing the thermosettable composition of claim
 35. 44. An article resulting from curing the thermosettable composition of claim
 36. 